An alignment apparatus for substrates comprises a first movement mechanism moving
a substrate to be treated in a horizontal direction, a second movement mechanism
moving the substrate in a vertical direction, a rotation mechanism rotating the
substrate in a substrate plane, an illumination tool irradiating the substrate
from a sidewise direction in a state where the substrate is held in a desired height
position by the second movement mechanism, an image sensor picking up an image
on a back surface of the substrate in an irradiated state, an edge position sensor
sensing plural edge positions of the substrate from an image obtained by the image
sensor, and a control computer obtaining a positional shift of the substrate based
on the edge positions sensed by the edge position sensor and correcting a positional
shift of the horizontal and rotation directions by the first movement and rotation mechanisms.
